1. Technical Field of the Invention
This invention relates to apparatus and method for changing dies, and a press dies for a plate reduction press machine.
2. Prior Art
1. FIGS. 1 and 2 show an example of a conventional plate reduction press machine; the machine comprises a frame 1 installed at a predetermined location on a transfer line S, provided with guide columns 3 such that the material to be pressed 2 can be moved inside the frame 1, a lower die holder 4 fixed substantially horizontally at the lower ends of the guide columns 3, an upper die holder 5 connected to the guide columns 3 so that it can be freely raised and lowered in opposition to the lower die holder 4 across the transfer line S, a crank shaft (not illustrated) located above the die holder 5, extending substantially horizontally in a direction orthogonal to the transfer line, and supported on the frame 1 by bearings on the non-eccentric portions, and a lower die 8 and an upper die 9 mounted on the lower die holder 4 and the upper die holder 5, respectively, facing each other, on opposite sides of the transfer line S.
The lower die holder 4 is provided with a dovetail groove 10 extending in the direction of the transfer line, on the upper surface, and a lower slide plate 12 coupled with the dovetail groove 10 in a freely movable manner and the lower die 8 is mounted on the upper surface of the slide plate 12 and coupled to it by means of a cotter pin 11.
The upper die holder 5 can move up and down with a reciprocating movement along the guide columns 3 when the crankshaft rotates, as the holder is supported and driven by an eccentric portion of the crankshaft. The holder is provided with a dovetail groove 13 extending in the direction of the transfer line, in its lower surface, and provided with an upper slide plate 15 engaging in a freely movable manner with the dovetail groove 13, and coupled to the upper die holder 5 by the cotter pin 14.
At the center of the upper slide plate 15, a through-hole 17 is bored with a peripheral groove 17a, and the upper die 9 installed. on the lower surface of the lower die support holder 18 is provided with a flange 18a that can engage with the peripheral groove 17a of the through-hole 17 and is inserted through the top of-the through-hole 17.
The crank shaft is connected to the output shaft (not illustrated) of a motor through a universal coupling and a speed reduction gear, and when the motor operates, the upper die holder 5 moves towards and away from the transfer line S, so that the upper die 9 mounted on the die holder 5 via the lower die support holder 18, also moves towards and away from the lower die 8.
When the material to be pressed 2 is pressed and formed in the direction of its thickness using the plate reduction press machine shown in FIGS. 1 and 2, the motor is operated and the crankshaft is rotated. Then, the material to be pressed 2 is inserted from the upstream A side of the transfer line, into the gap between the upper die 9 and the lower die 8. The material to be pressed 2 moves from the upstream A side of the transfer line along the transfer line S towards the downstream Side B of the transfer line, while the material is pressed and shaped in the direction of its thickness by the upper die 9 that moves towards and away from the transfer line S according to the movement of the eccentric portion of the crank shaft.
When the lower die 8 is to be replaced, the cotter pin 11 that locates the lower slide plate 12 in the lower die holder 4 is removed, the lower slide plate 12 is pulled out along the dovetail groove 10 of the lower die holder 4, the lower die 8 is moved out of the plate reduction press machine, the lower die 8 mounted on the lower die holder 4 is released from the lower die holder 4, and then the lower die 8 is lifted up by a hoist not illustrated and transferred to another predetermined site. Using the same hoist, a new lower die 8 is then lifted up, carried over the lower slide plate 12 and mounted there, and then the lower slide plate 12 is pushed into the center of the plate reduction press machine along the dovetail groove 10 of the lower die holder 4, and locked on the lower die holder 4 using the cotter pin 11.
When the upper die 9 is to be replaced, the cotter pin 14 that locates the upper slide plate 15 to the upper die holder 5 is removed, the upper slide plate 15 is pulled out along the dovetail groove 13 of the upper die holder 5, and is moved out of the plate reduction press machine, the upper die support holder 18 incorporated in the upper slide plate 15 is lifted up by a hoist not illustrated and taken to another predetermined site, and after the upper die 9 is removed from the die support holder 18, a new upper die 9 is mounted on the upper die support holder 18, and then the die support holder 18 is lifted up by the hoist and carried above the upper slide plate 15, and after the holder 18 is positioned in the through-hole 17 of the upper slide plate 15, the slide plate 15 is pushed in along the dovetail groove 13 of the upper die holder 5, into the center of the plate reduction press machine, and then locked in the upper die holder 5 by the cotter pin 14.
However, with the plate reduction press machine shown in FIGS. 1 and 2, the wear of the lower and upper dies 8, 9 is so severe that each die 8 or 9 must be replaced frequently. Consequently, unless the dies are often replaced, the specified capacity of the plate reduction press machine, even if it has a high efficiency, cannot be achieved, and this is a problem.
2. Conventionally, a rough rolling mill is used to roll a slab. The slab to be rolled may be as short as 5 m to 12 m, and a plurality of rough rolling mills are required to roll the slab or the slab must be rolled backwards and forwards in a reversing rolling system, to obtain the predetermined thickness of the slab. In addition, it is planned to use a reduction press machine of which an example is shown in FIG. 3. The example shows a case in which cranks and connecting rods are used; the cranks 104 are connected to the dies 102 installed above and below the slab 101, through connecting rods 103, and the dies 102 are moved up and down to press on the slab. The slab 101 is moved by pinch rolls 106 and the transfer table 107.
Recently, a continuous casting system has been introduced to produce a long slab, so it is necessary to move the slab continuously to a reduction press machine after it leaves the casting system. When a slab is rough rolled with a rough rolling mill, there is a minimum nip angle (about 17 .infin.), and the permissible reduction .DELTA. t per rolling operation is about 50 mm. Reversing rolling cannot be applied because the slab is continuous, therefore to achieve a predetermined thickness, it is necessary to provide a plurality of rough rolling mills in series, or if one rolling machine is used, the diameter of the working rolls must be made much greater. However, such a rough rolling mill with large diameter rolls is difficult to design and manufacture because of its high cost, and furthermore rolls with a large diameter must rotate at a low speed so that the rolls cannot be cooled easily, which results in a short life for the rolls. When a reduction press machine with cranks and connecting rods is used, the slab must be continuously moved even during pressing, so the slab is moved by pulling it with pinch rolls. As a result, there is a large load on the pinch rolls, which makes the size of the entire system large. Consequently, there are many problems with vibration and cost.
To solve these problems, the inventors of the present invention, invented and applied for a patent for the "Thickness reduction press machine" (unexamined Japanese patent application No.10-42328). This machine is shown in FIG. 4 and comprises dies 102 provided above and below the slab 101, a slider 108 provided for each die to give the die an up and down and backwards and forwards motion, and a drive system to drive these sliders. The aforementioned sliders are provided with a main unit 108a in which circular holes are bored with center lines at right angles to the direction of the slab, these circular holes with axes 109a engage with, cranks 109 (eccentric axes) with second axes 109b and a diameter less than the diameter of the holes, and the center lines of these axes are displaced from those of the holes. These cranks are rotated by the above-mentioned drive system.
With this configuration, when the cranks are rotated, the axes of the circular holes are cranked around the center line of the second set of axes, and this transmits an upwards and downwards and backwards and forwards movement to the main unit 108a. Thereby, the slider 108 can press the dies and give a forward movement to the dies during pressing, so that the slab 101 is pushed forwards (in the direction of drawing the slab) during pressing, so enabling a continuous pressing operation. In addition, according to this invention, the slab 101 is pressed by dies 102 from both above and below, so a large rolling reduction can be attained.
Although the aforementioned plate reduction press machine provides a large rolling reduction and can press a slab continuously, there is a proportionally severe wear on the upper and lower dies, possibly resulting in shorter intervals for replacing dies. As known in the prior art, there are die changing systems for reduction press machines, stentering machines, etc. However, even if any of the systems is adapted for use in a plate reduction press machine, there is the problem that excessive time and labor are spent in replacing dies.
3. Moreover, conventional reduction press machines such as slab presses that reduce the thickness of a slab, stentering presses that compress a slab laterally, or forging presses, incorporate dies that are constructed integrally.
When a high-temperature material, e.g. a slab, is compressed using a thickness reduction press, the temperatures of the dies are not distributed evenly in the direction of breadth (lateral direction of the slab), so the dies may often deform or crack. In addition, the sides of the center portion of the dies wear more than both ends. Therefore, when the center portion wears by a predetermined amount, the dies must be replaced even if both ends have not worn so much. When the size of the dies is large, integral dies cannot be manufactured easily, and they also become expensive.